The present invention relates generally to current sensing devices for electrical systems, and more particularly to alternating current fault indicators for use within closed housings such as are utilized to enclose pad-mounted components in an underground power distribution system.
Various types of self-powered fault indicators have been constructed for detecting electrical faults in power distribution systems, including clamp-on type fault indicators, which clamp directly over cables in the systems and derive their operating power by inductive coupling to the monitored conductor, and test point type fault indicators, which are mounted over test points on cables or associated connectors of the systems and derive their operating power by capacitively coupling to the monitored conductor. Such fault indicators may be either of the manually reset type, wherein it is necessary that the inductors be physically reset, or of the self-resetting type, wherein the indicators are reset upon restoration of line current. Examples of such fault indicators are found in products manufactured by E. O. Schweitzer Manufacturing Co. of Mundelein, Ill., and in U.S. Pat. Nos. 3,676,740, 3,906,477, 4,063,171, 4,234,847, 4,375,617, 4,438,403, 4,456,873, 4,458,198, 4,495,489, and 5,677,678 of the present inventor.
Detection of fault currents in fault indicators is typically accomplished by means of a magnetic reed switch in close proximity to the conductor being monitored. Upon occurrence of a fault current, an abnormally high magnetic field is induced around the conductor. As a result, the contacts of the magnetic reed switch close and actuate trip or fault circuitry which magnetizes an internal pole piece to position a target indicator, which is visible from the exterior of the indicator, to a trip or fault indicating position.
In certain applications, such as where the fault indicator is installed in a dark or inaccessible location, it would be beneficial if the indication of a fault were accomplished by means of a light source. More specifically, when the circuit monitoring module of the fault indicator is located in an inacessible location, such as within an equipment or system component enclosure, it would be beneficial if the fault indication were accomplished by means of a light source within easy view and preferably viewable from outside the enclosure. Under such circumstances, fault indication is easy, particularly when dark. Repair crews can then more easily find the location of the fault.
In those applications, it would be beneficial if the fault indicator included circuitry that would automatically reset the light indication of the fault occurrence upon the expiration of a predetermined period of time, yet would provide the light indication for such predetermined period of time, irrespective of whether normal line current is restored to the monitored conductor. Moreover, in this same application, it would be beneficial if the fault indicator included circuitry that permitted manual reset of the light indication upon demand. Such circuitry would conserve the finite energy available from the battery or other energy source connected to the light source.
Because of the compact construction and limited power available in self-powered fault indicators, it is preferable that the light indication be provided with the minimal additional circuitry and structure within the fault indicator which would provide reliable and extended operation following an occurrence of a fault.
With the increased use of underground electrical distribution systems using primary and secondary feeder cables which are directly buried in the ground and brought to the surface only for connection to pad-mounted distribution transformers or other system components, the need has arisen for fault indicators suitable for mounting within the above-ground metal enclosures typically utilized to house and protect such components. Preferably, such fault indicators should be sufficiently compact so as to not interfere with other components in the enclosures. Further, such indicators would preferably indicate the occurrence of a fault current in a manner permitting a lineman to view the circuit status without having to open the enclosure. Additionally, such indicators, which would typically require use of a lithium battery or similar energy source, would preferably include means for testing whether the battery has sufficient energy to illuminate the connected light source.
In addition, such indicators would preferably include timed reset circuitry for resetting the light indication upon expiration of a predetermined period of time. This circuitry would allow light indication of the occurrence of a fault current for a predetermined period of time after such occurrence, even after normal line current is restored in the monitored conductor. Furthermore, such indicators would preferably include a manual reset circuit for resetting the light indication of a fault current upon demand.
The present invention is directed to a novel fault indicator which meets the above requirements by utilizing a magnetic winding, such as the actuator winding of the electro-mechanical indicator flag assembly typically utilized in fault indicators, in conjunction with a magnetic circuit which, upon occurrence of a fault, connects an internal battery to a light source mounted to an equipment enclosure and viewable external thereof. The present invention is also directed to a fault indicator of the type described above wherein the fault indicator includes a timed reset circuit for automatically resetting the light indication of the fault occurrence upon expiration of a predetermined period of time. The present invention is further directed to a fault indicator of the type described above wherein the fault indicator includes a manual reset circuit for manually resetting the light indication of the fault occurrence upon demand. Both reset circuits conserve the finite energy available from the battery or other energy source connected to the light source.
The present invention is further directed to a fault indicator for detection of faults within an equipment enclosure, such as the type used to house pad-mounted transformers and other system components in an electrical distribution system, wherein fault indications are provided at a light indicator viewable external of the enclosure, thereby obviating the need for visual contact with the interior of the enclosure. Additionally, the present invention is directed to a fault indicator of the type described above wherein the fault indicator includes means for testing whether the energy level of the energy source is sufficient to illuminate the. connected light source.
Accordingly, it is a general object of the present invention to provide a new and improved fault indicator for use in conjunction with enclosed pad-mounted power distribution system components.
It is another object of the present invention to provide a new and improved fault indicator having a light indication of fault occurrence.
It is another object of the present invention to provide a compact and economical fault indicator which provides an indication of circuit status at a light indicator located remote from the circuit monitoring module of the fault indicator.
It is yet another object of the present invention to provide a fault indicator wherein a light indication is provided utilizing a remote fault indicator light module in conjunction with an internal battery.
It is another object of the present invention to provide a fault indicator wherein the light indication of a fault occurrence may be automatically reset upon the expiration of a predetermined period of time to provide indication of such fault occurrence during such predetermined period of time, irrespective of whether normal line current has been restored to the monitored cable, which also conserves the finite energy available from the battery or other energy source connected to the light source.
It is still another object of the present invention to provide a fault indicator wherein the light indication of the fault occurrence may be manually reset upon demand, such as after viewing the light indication, thereby conserving the finite energy available from the battery or other energy source connected to the light source.
It is yet another object of the present invention to provide a fault indicator utilizing a remote fault indicator light module in conjunction with an internal battery wherein the fault indicator includes means for testing whether the energy level of the internal battery is sufficient to illuminate the light source contained within the remote fault indicator light module.
The present invention is directed to a fault indicator that provides indication of a fault current outside the exterior surface of an electrical equipment enclosure. The fault indication is presented following the occurrence of a fault current in an electrical conductor within the enclosure. The fault indicator includes a circuit monitoring module and a remote fault indicator light module operatively connected thereto. The remote fault indicator light module is mounted to the exterior surface of the enclosure. A battery is contained within the circuit monitoring module and a light source is contained within the remote fault indicator light module. The light source is operable from the battery.
A magnetic circuit is included in the fault indicator, which includes a magnetic pole piece, a magnetically actuated switch and a bias magnet. The bias magnet has a permanent magnetic polarity which opposes a magnet field in the magnet pole piece in one direction, and reenforces a magnetic field in the magnetic pole piece in the other direction. As a result, the magnetically actuated switch is conditioned to open in response to a magnetic field in one direction and close in response to a magnetic field in the other direction.
The fault indicator further includes circuit means having a magnetic winding in magnetic communication with the magnetic pole piece. The winding is responsive to the current in the monitor conductor for developing a magnetic field in the pole piece in one direction to condition the magnetically actuated switch open during normal current flow in the monitored conductor. The winding also develops a magnetic field within the pole piece in the opposite direction to condition the magnetically actuated switch closed upon occurrence of a fault current in the conductor. The magnetically actuated switch is connected between the battery and light source to cause the light source to be illuminated upon the occurrence of a fault current.
The fault indicator further includes reset circuitry, such as a timed reset circuit for automatically resetting the light indication of the fault occurrence upon the expiration of a predetermined period of time. The fault indicator may further include a manual reset circuit for manually resetting the light indication of the fault occurrence upon demand. The manual reset circuit may comprise a magnetically actuated switch contained within the remote fault indicator light module wherein the switch is connected to a timing capacitor included within the timed reset circuit.
The remote fault indicator light module may have a bolt-shaped housing, which includes a transparent head. Further, the light source may comprise a light emitting diode and a flasher circuit may cause the light emitting diode to flash.
In another aspect of the present invention, another magnetically actuated switch may be contained within the remote fault indicator light module to connect the battery to the light source. This additional magnetically actuated switch permits a lineman to test the sufficiency of the energy level of the battery and determine whether the battery is capable of causing illumination of the light emitting diode or other light source.